Peroxynitrite scavenging by Campylobacter jejuni truncated hemoglobin P

Area of Science:

• Biochemistry
• Microbiology
• Protein Science

Background:

• Truncated hemoglobins (trHbs) are found across diverse organisms, including bacteria like Campylobacter jejuni.
• These proteins play roles in protecting microorganisms from reactive oxygen and nitrogen species within host environments.
• trHbs are classified into four phylogenetic groups (I-IV) based on their 2-on-2 globin fold.

Purpose of the Study:

• To investigate the kinetics and mechanism of peroxynitrite scavenging by ferric Campylobacter jejuni truncated hemoglobin P (Cj-trHbP).
• To determine the influence of carbon dioxide (CO2) and pH on the scavenging activity of Cj-trHbP.
• To assess the protective role of Cj-trHbP against peroxynitrite-mediated L-tyrosine nitration.

Main Methods:

• Stopped-flow UV-Vis spectroscopy was used to monitor peroxynitrite disappearance.
• Kinetic assays were performed at varying pH (6.3-7.9) and in the presence/absence of CO2.
• The formation of nitro-L-tyrosine was quantified to evaluate the inhibition of L-tyrosine nitrosylation.

Main Results:

• Cj-trHbP rapidly scavenges peroxynitrite, indicated by spectral changes at 302 nm.
• CO2 did not affect the scavenging rate of Cj-trHbP but influenced peroxynitrite's spontaneous decay.
• Peroxynitrite scavenging by Cj-trHbP is enhanced at lower pH, suggesting peroxynitrous acid is the reactive species.
• Cj-trHbP effectively inhibits L-tyrosine nitrosylation, protecting against peroxynitrite-induced nitration.

Conclusions:

• Cj-trHbP exhibits high reactivity towards peroxynitrite, attributed to its active site metal center.
• The findings suggest Cj-trHbP contributes to the survival of Campylobacter jejuni in host environments by neutralizing harmful reactive nitrogen species.
• This study elucidates the protective mechanisms of truncated hemoglobins against oxidative stress in pathogenic bacteria.